Pentenoic acid hydroxycarbonylation method

ABSTRACT

The invention discloses pentenoic acid hydroxycarbonylation into adipic acid. More particularly, it concerns one pentenoic acid hydroxycarbonylation method involving reaction water and carbon monoxide, in the presence of a catalyst comprising at least rhodium and/or iridium and an iodinated or brominated catalytic promoter. In the method, the catalyst is derived at least in part from a previous pentenoic acid hydroxycarbonylation operation. The reaction is effected in the presence of an amount of branched carboxylic diacids having 6 carbon atoms not exceeding 200 grams per kilogram reaction mixture.

The present invention relates to the hydroxycarbonylation of pentenoicacids to adipic acid.

During the hydroxycarbonylation of pentenoic acids, principally3-pentenoic acid, in the presence of a catalyst and a promoter, to giveadipic acid, there are minor but nevertheless significant amounts ofbranched carboxylic diacids which are isomers of adipic acid,essentially 2-methylglutaric acid and 2-ethylsuccinic acid, as well astraces of 2,2-dimethylsuccinic acid.

Following separation of the adipic acid, the unconverted pentenoic acid,the catalyst, the promoter and various byproducts, such asgamma-valerolactone, are recycled into the hydroxycarbonylation reactor.

However, although it is advantageous in terms of the economics of theprocess to recycle to best effect the unconverted pentenoic acid, thecatalyst, the promoter and the byproducts which are capable of beingconverted, at least partially, to adipic acid, the applicant has foundthat the recycling of excessively large amounts of branched carboxylicdiacids has an adverse effect on the activity of the catalyst in thehydroxycarbonylation reaction of pentenoic acid.

Besides this effect of deactivating the catalyst, the presence ofbranched diacids is clearly harmful to the purity of the adipic acid, inparticular by its trapping of the metal catalyst during thecrystallization of the said adipic acid.

The present invention therefore relates more particularly to a processfor hydroxycarbonylating pentenoic acid by reaction with water andcarbon monoxide in the presence of a catalyst comprising at leastrhodium and/or iridium and of an iodine- or bromine-containing promoter,in which process the catalyst originates at least in part from a prioroperation of hydroxycarbonylation of pentenoic acid, characterized inthat the reaction is carried out in the presence of an amount ofbranched carboxylic diacids having 6 carbon atoms of less than or equalto 200 grams per kilogram of reaction mixture.

The terms branched carboxylic diacids and branched diacids areequivalent in the present text and also embrace the anhydride formscorresponding to these diacids.

In the process according to the invention the hydroxycarbonylationreaction is preferably conducted in the presence of an amount ofbranched carboxylic diacids having 6 carbon atoms of less than or equalto 150 grams per kilogram of reaction mixture.

The pentenoic acid is hydroxycarbonylated in the presence of a catalystcomprising rhodium and/or iridium and, optionally, other noble metalsselected from ruthenium and osmium. The amount of catalyst to beemployed can vary within wide limits.

In general an amount, expressed in moles of metallic iridium and/ormetallic rhodium per liter of reaction mixture, of between 10⁻⁴ and 10⁻¹gives satisfactory results. Smaller amounts can be employed; however, itis observed that the rate of reaction is low. Larger amounts aredisadvantageous only from an economic standpoint.

The concentration of iridium and/or rhodium is preferably between 5×10⁻⁴and 10⁻² mol/liter.

By iodine- or bromine-containing promoter is meant, in the context ofthe process of the invention, HI and HBr and organic iodine compounds ororganic bromine compounds which are capable of generating HI or HBrunder the reaction conditions, and more particularly alkyl iodides andalkyl bromides having 1 to 10 carbon atoms. Methyl iodide and methylbromide are recommended more particularly.

The promoter used is preferably an iodine-containing promoter and, morepreferably, is HI or methyl iodide.

The amount of iodine- and/or bromine-containing promoter to be employedis generally such that the molar ratio of iodine (and/or bromine) toiridium (and/or rhodium) is greater than or equal to 0.1. It isgenerally preferable for this ratio to be less than or equal to 20.Preferably, the molar ratio of iodine (and/or bromine) to iridium(and/or rhodium) is between 1 and 5.

The presence of water is vital for conducting the hydroxycarbonylation.Generally speaking, the amount of water to be employed is such that themolar ratio of water to pentenoic acids is between 0.01 and 10.

A larger amount is undesirable owing to the loss in catalytic activitywhich is observed. At a given point in time the molar ratio of water topentenoic acids in the reaction mixture may be less than the minimumvalue indicated above if the reaction is carried out, for example, withcontinuous injection of water rather than with the introduction of watertogether with the other charges before the hydroxycarbonylationreaction.

The molar ratio of water to pentenoic acids is preferably between 0.01and 2, subject to the above comment regarding the minimum value.

The hydroxycarbonylation reaction can be carried out either in aseparate solvent or in a large excess of pentenoic acids.

As a separate solvent it is possible in particular to use saturatedaliphatic or aromatic carboxylic acids containing not more than 20carbon atoms, provided that these acids are liquid under the reactionconditions. As examples of such carboxylic acids mention may be made ofacetic, propionic, butyric, valeric, adipic, benzoic and phenylaceticacids.

The separate solvent can also be selected from saturated aliphatic orcycloaliphatic hydrocarbons and their chlorinated derivatives andaromatic hydrocarbons and their chlorinated derivatives, provided thatthese compounds are liquid under the reaction conditions. As examples ofsuch solvents mention may be made of benzene, toluene, chlorobenzene,dichloromethane, hexane and cyclohexane.

When present in the reaction mixture the separate solvent makes up, forexample, from 10 to 99% by volume relative to the total volume of thesaid reaction mixture and, preferably, from 30 to 90% by volume.

In a preferred variant the hydroxycarbonylation reaction is carried outin the pentenoic acids themselves, namely 2-pentenoic, 3-pentenoic and4-pentenoic acids and mixtures thereof.

The hydroxycarbonylation reaction is conducted at a pressure which isgreater than atmospheric pressure, and in the presence of carbonmonoxide. It is possible to use substantially pure carbon monoxide ortechnical-grade carbon monoxide as is found in commerce.

The reaction is conducted in the liquid phase. The temperature isgenerally between 100 and 240° C. and preferably between 160 and 200° C.

The total pressure can vary within wide limits. The partial pressure ofcarbon monoxide, measured at 25° C., is generally from 0.5 to 50 bar andpreferably from 1 to 25 bar.

As indicated above, the reaction mixture obtained from thehydroxycarbonylation reaction comprises essentially the unconvertedpentenoic acids, water, the iodine- and/or bromine-containing promoter,the catalyst, the solvent (if employed), the resultant adipic acid, andthe other byproducts, which are formed in greater or lesser quantities,such as, for example, 2-methylglutaric, 2-ethylsuccinic and valericacids and gamma-valerolactone (or 4-methylbutyrolactone).

The at least partial separation of the branched diacids such that theirconcentration after recycling into the hydroxycarbonylation reactor doesnot exceed the upper limits indicated above, throughout the reaction,can be carried out by known methods. It is possible, for example, toconvert all or some of the branched diacids into their correspondinganhydrides, as is described in the patent EP-A-0 687 663, in order toenable them to be separated more easily by distillation.

It is also possible to subject the reaction mixture which is obtainedfrom the hydroxycarbonylation to fractional distillation and to removethe lightest compounds, such as the pentenoic acids or the othercompounds having 5 carbon atoms. This first distillation can be carriedout under atmospheric pressure directly or following separation of partof the resultant adipic acid by crystallization. Subsequently, thefractions richest in branch diacids can be distilled. This distillationcan be supplemented by other operations for separating the variousconstituents of the reaction mixture obtained from thehydroxycarbonylation. In this way it is possible to carry outcrystallization, and optionally one or more recrystallizations, of theadipic acid in order to recover as much as possible of the catalystwhich it contains.

The branched diacids are distilled under reduced pressure, possibly andadvantageously under a gentle stream of carbon monoxide.

It is possible in this way to recycle at least some of the catalyst, ofthe promoter and of the light compounds capable of being converted atleast in part into adipic acid, while recycling only very little if anyof the branched diacids.

Advantageously, the process of the invention is performed continuously.Indeed, apart from the obvious industrial advantage of this type ofimplementation, it is much easier to permanently maintain a relativelylow level of branched diacids, the unavoidable formation of the saidbranched diacids and their partial recycling being compensated by thecontinuous withdrawal of a portion of the reaction mixture.

The concentration of branched diacids in the reaction mixture can thenbe maintained, for example, at a level of less than or equal to 100grams per kilogram and, preferably, of less than or equal to 50 gramsper kilogram.

Finally, among the branch diacids, it is found that it is even moreadvantageous for 2-ethylsuccinic acid to be maintained more specificallyand within the reaction medium at a content of less than or equal to 50grams per kilogram and, preferably, of less than or equal to 30 gramsper kilogram. In the context of a continuous process, this content of2-ethylsuccinic acid can then be maintained in the reaction medium at alevel of less than or equal to 20 grams per kilogram and, preferably, ofless than or equal to 10 kilograms per kilogram.

The examples which follow illustrate the invention.

EXAMPLES 1 TO 3

A 1 liter metal reactor equipped with means for heating and cooling,with a stirrer (operating at 1200 revolutions/minute), with devices forintroducing the reactants and for withdrawal, and with devices formeasuring the temperature and pressure is charged with:

2.52 mol of 3-pentenoic acid (P3)

0.924 mmol of IrCl(COD)

2.24 mmol of HI (57% by weight aqueous solution)

A pressure of 5 bar of CO is established at room temperature and thenthe reaction mixture is heated with stirring to 185° C., at whichtemperature the pressure is adjusted to 20 bar using CO. 22.7 g of water(1.26 mol) are then injected over 30 minutes.

After 30 minutes reaction, the reaction mixture is removed while stillhot, under a carbon monoxide atmosphere, into a 500 ml pan.

A sample of this mixture is assayed by gas chromatography (GC) andhigh-performance liquid chromatography (HPLC).

The results are as follows:

degree of conversion (DC) of P3: 52%

yield (Y) of adipic acid (AdOH) relative to P3 converted: 68%

yield (Y) of branched diacids (2-methylglutaric and 2-ethylsuccinicacid) relative to P3 converted: 13%

yield (Y) of gamma-valerolactone (M4L) relative to P3 converted: 8%

rate of absorption of CO in moles per hour per liter of reaction mixture(approximately 280 ml): 5.8

linearity (L) (=ratio of adipic acid to total diacids obtained): 84%.

The mixture withdrawn is distilled using a column with a height of 250cm, under atmospheric pressure, with CO being bubbled through.

This gives a fraction comprising unconverted pentenoic acid,gamma-valerolactone, valeric and methylbutanoic acids, and a portion ofmethylglutaric and ethylsuccinic acids.

Methylglutaric and ethylsuccinic acids are subsequently distilled underreduced pressure (with CO being bubbled through via a capillary tube).

The residue essentially contains adipic acid and the catalyst. Thecatalyst is recovered in the recrystallization and wash waters of theadipic acid.

After having replenished the catalyst and added the iodine-containingpromoter and 3-pentenoic acid again, the hydroxycarbonylation ofpentenoic acid is repeated as described above, with substantially thesame amounts of reactants and under the same operating conditions, butwith recycling of a portion of the branched diacids isolated beforehand.

The charges are as follows:

2.44 mol of 3-pentenoic acid (P3)

0.924 mmol of IrCl(COD)

2.24 mmol of HI (57% by weight aqueous solution)

11.5 g of branched diacids (41 g/kg of initial reaction mixture)

1.26 mol of water (22.7 g) injected over 30 minutes.

The reaction lasts for 30 minutes at 185° C., and quantitativedetermination gives the following results.

degree of conversion (DC) of P3: 53%

yield (Y) of adipic acid (AdOH) relative to P3 converted: 66%

yield (Y) of branched diacids (2-methylglutaric and 2-ethylsuccinicacid) relative to P3 converted: 15.5%

yield (Y) of gamma-valerolactone (M4L) relative to P3 converted: 8%

rate of absorption of CO in moles per hour per liter of reaction mixture(approximately 280 ml): 5.8

linearity (L) (=ratio of adipic acid to total diacids obtained): 81%

total content of branched diacids in the final reaction mixture: 134g/kg.

The treatment described for Example 1 is carried out and, after thecatalyst has been replenished and the iodine-containing promoter and3-pentenoic acid have been added again the hydroxycarbonylation ofpentenoic acid is repeated as described above, with substantially thesame amounts of reactants and under the same operating conditions, butwith recycling of a larger amount of the branched diacids isolatedbeforehand.

The charges are as follows:

2.35 mol of 3-pentenoic acid (P3)

0.924 mmol of IrCl(COD)

2.24 mmol of HI (57% by weight aqueous solution)

22.9 g of branched diacids (41.5 g/kg of initial reaction mixture)

1.26 mol of water (22.7 g) injected over 30 minutes.

The reaction lasts for 30 minutes at 185° C., and quantitativedetermination gives the following results.

degree of conversion (DC) of P3: 49%

yield (Y) of adipic acid (AdOH) relative to P3 converted: 65%

yield (Y) of branched diacids (2-methylglutaric and 2-ethylsuccinicacid) relative to P3 converted: 18.3%

yield (Y) of gamma-valerolactone (M4L) relative to P3 converted: 7%

rate of absorption of CO in moles per hour per liter of reaction mixture(approximately 280 ml): 5.2

linearity (L) (=ratio of adipic acid to total diacids obtained): 78%

total content of branched diacids in the final reaction mixture: 177g/kg.

In the results obtained in Example 3, with a content of branched diacidsof between 81.5 g/kg at the beginning of the hydroxycarbonylation and177 g/kg at the end of the hydroxycarbonylation, it is observed that therate of reaction and the linearity are beginning to decrease.

COMPARATIVE TEST 1

The recycling tests are repeated, with the introduction of largeramounts of methylglutaric and ethylsuccinic acids, the operatingconditions being the same.

The charges are as follows:

2.21 mol of 3-pentenoic acid (P3)

0.924 mmol of IrCl(COD)

2.24 mmol of HI (57% by weight aqueous solution)

45.8 g of branched diacids (158 g/kg of initial reaction mixture)

1.26 mol of water (22.7 g) injected over 30 minutes.

The reaction lasts for 30 minutes at 185° C., and quantitativedetermination gives the following results.

degree of conversion (DC) of P3: 29%

yield (Y) of adipic acid (AdOH) relative to P3 converted: 53%

yield (Y) of branched diacids (2-methylglutaric and 2-ethylsuccinicacid) relative to P3 converted: 31.1%

yield (Y) of gamma-valerolactone (M4L) relative to P3 converted: 4%

rate of absorption of CO in moles per hour per liter of reaction mixture(approximately 280 ml): 2.8

linearity (L) (=ratio of adipic acid to total diacids obtained): 63%

total content of branched diacids in the final reaction mixture: 257g/kg.

In the results obtained in Comparative Test 1, with a content ofbranched diacids of between 158 g/kg at the beginning of thehydroxycarbonylation and 257 g/kg at the end of thehydroxycarbonylation, it is observed that the rate of reaction and thelinearity of the diacids obtained decrease very greatly.

What is claimed is:
 1. A process for hydroxycarbonylating pentenoic acidby reaction with water and carbon monoxide in the presence of a catalystcomprising at least rhodium and/or iridium and of an iodine-containingand/or bromine-containing promoter, comprising recycling in the reactionmixture at least part of the unreacted pentenoic acid, the catalyst andthe promoter contained in the final reaction mixture, wherein, beforerecycling the unreacted pentenoic acid, the catalyst and the promoter,at least a part of the branched carboxylic diacids having 6 carbonsproduced by the hydroxycarbonylation reaction is separated and notrecycled together with the unreacted pentenoic acid, catalyst andpromoter in order to maintain the amount of said branched carboxylicdiacids at a level less than or equal to 200 grams per kilogram ofreaction mixture.
 2. The process according to claim 1, wherein thehydroxycarbonylation reaction is conducted in the presence of an amountof branched carboxylic diacids having 6 carbon atoms of less than orequal to 150 grams per kilogram of reaction mixture.
 3. The processaccording to claim 1, wherein the hydroxycarbonylation reaction iscarried out in the presence of a catalyst comprising rhodium and/oriridium or, optionally, other noble metals selected from ruthenium andosmium.
 4. The process according to claim 1, wherein the concentrationof catalyst employed, expressed as moles of metallic iridium and/ormetallic rhodium per liter of reaction mixture, is between 10⁻⁴ and 10⁻¹mole/liter.
 5. The process according to claim 1, wherein the iodine-and/or bromine-containing promoter comprises HI, HBr, organic iodinecompounds or organic bromine compounds which are capable of generatingHI or HBr under the reaction conditions.
 6. The process according toclaim 1, wherein the promoter used is an iodine-containing promoter. 7.The process according to claim 1, wherein the molar ratio of iodineand/or bromine promoter to iridium and/or rhodium catalyst is greaterthan or equal to 0.1.
 8. The process according to claim 1, wherein themolar ratio of water to pentenoic acids is between 0.01 and
 10. 9. Theprocess according to claim 1, wherein the hydroxycarbonylation reactionis conducted either in a separate solvent or in a large excess ofpentenoic acids.
 10. The process according to claim 9, wherein theseparate solvent comprises saturated aliphatic or aromatic carboxylicacids containing not more than 20 carbon atoms, saturated aliphatic orcycloaliphatic hydrocarbons and their chlorinated derivatives, oraromatic hydrocarbons and their chlorinated derivatives, provided thatthese compounds are liquid under the reaction conditions.
 11. Theprocess according to claim 1, which is performed continuously, andwherein the concentration of branched diacids in the reaction mixture isless than or equal to 100 grams per kilogram of reaction mixture. 12.The process according to claim 4, wherein the concentration of catalystemployed is between 5×10⁻⁴ and 10⁻² mole/liter.
 13. The processaccording to claim 5, wherein the iodine- and/or bromine-containingpromoter comprises alkyl iodides and/or alkyl bromides having 1 to 10carbon atoms.
 14. The process according to claim 6, wherein the promotercomprises HI or methyl iodide.
 15. The process according to claim 7,wherein the molar ratio of iodine and/or bromine promoter to iridiumand/or rhodium catalyst is less than or equal to
 20. 16. The processaccording to claim 11, wherein the concentration of branched diacids inthe reaction mixture is less than or equal to 50 grams per kilogram ofreaction mixture.